1. Field of the Invention
The present invention relates to an apparatus for generating L-band light source and an optical signal amplifier, specifically, relates to an apparatus for generating L-band light source by increasing amplification gain against an L-band light to execute a stable resonating operation, and to an optical amplifier which amplifies L-band light signal efficiently.
2. Discussion of Related Art
In general, an optical transmission apparatus uses a wavelength band of approximately 1530 nm to 1560 nm, such as commercial band C-band or middle band M-band, which is caused by characteristics of optical amplifier for amplifying optical signal transmitted mostly through optical line. At present, the optical amplifier is configured in a manner that a pumping light of 980 nm or 1480 nm is supplied with an erbium-doped-fiber EDF doped with a rare earth ion such as erbium. As shown in FIG. 1, a graph showing amplification gain characteristics of the optical fiber amplifier, the optical fiber amplifier provides an efficient amplification gain in a wavelength band of approximately 1530 nm to 1560 nm. Meanwhile, the optical transmission system using C-band needs an apparatus for generating a light source having corresponding wavelength band. In general, the light source generating apparatus uses a semi-conductor laser device or the erbium-doped-fiber EDF. The light source generating apparatus using ELF has a ring-type structure generally which returns amplified signal output from the EDF back to the EDF through a specific tunable filter.
FIG. 2 is a block diagram of a conventional light source generating apparatus having the ring-type structure. Reference numeral 1 denotes a pumping laser diode which outputs pumping light of 980 nm or 1480 nm, for example. Pumping light output from the pumping laser diode 1 is input to an erbium-doped-fiber EDF 3 through a wavelength division multiplexer WDM 2. Then, optical signal output from the EDF 3 is input to a tunable filter 5 through an isolator 4 which passes a specific wavelength light. The specific wavelength light output from the tunable filter 5 is returned back to the EDF 3 by way of a tap coupler 6, an isolator 7 and the wavelength division multiplexer WDM 2. The tap coupler 6 divides optical signal output from the tunable filter 5 in a predetermined ratio, for example 70:30, and outputs the 70% light as an output light and the 30% light to the isolator 7 as an input. In the above configuration, it is possible to form a resonating structure for a specific wavelength light by returning the amplified light output from the EDF 3 back to the EDF 3 through the tunable filter 5, and to obtain the specific wavelength light by outputting the amplified light through the tap coupler 6.
Meanwhile, as optical communication techniques have been developed rapidly, a wavelength division multiplexing WDM transmission technique for transmitting optical signal having plural wavelengths through one optical line simultaneously has been widely used so as to increase transmission efficiency of the optical line. Accordingly, the wavelength division multiplexing WDM system requires methods for transmitting a large number of wavelengths, i.e., channels through a single optical line at a time. However, as described above, it is very difficult to secure a large number of channels more than a predetermined number since the available wavelength band in the present optical transmission system is confined within 1530 nm to 1560 nm due to the amplification characteristics of the optical fiber amplifier. In consideration of the above obstacle, an advanced methods has been studied for transmitting optical signal using a L-band, i.e., a wavelength of 1570 nm to 1610 nm, no the C-band. By this means, it is considered to increase the amplification efficiency of L-band light by altering the length of the EDF 3. That is, the L-band gain of the EDF 3 is increased according as the EDF 3 is lengthened. For example, if the length of the EDF 3 is 21 m, the gain is increased against the wavelength of 1530 nm to 1560 nm, if the length is 100 m, the gain is increased against the wavelength of 1570 nm to 1610 nm. However, since it is also impossible to obtain more than a maximum xe2x88x9250 dB output power by supplying a normal pumping light even though the EDF 3 is lengthened to increase the amplification gain of L-band light, it is readily appreciated that the above method is inadequate to amplify the L-band light. Besides, in the light source generating apparatus having the ring-type structure as shown in FIG. 2, a light having a wavelength more than 1600 nm is not resonated and the gain is decreased since the amplification gain of L-band is very weak as shown in FIG. 1. Consequently, it is impossible to generating L-band light by using the EDF 3.
Accordingly, the present invention is directed to an apparatus for generating L-band light source using optical fiber, and an optical amplifier that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus for generating L-band light source using optical fiber amplification.
Another object of the present invention is to provide an optical amplifier which can amplify L-band light efficiently using optical fiber amplifiers.
Another object of the present invention is to provide an apparatus for generating L-band light source and an optical amplifier which has a single structure so as to be alternatively used as the apparatus for generating L-band light source or the optical amplifier.
To accomplish an object in accordance with a first embodiment of the present invention, there is provided an apparatus for generating L-band light source using optical fiber comprising, in accordance with a first embodiment of the invention comprising: a first optical fiber amplifier for supplying a maximum amplification gain against an input light having a wavelength of 1530 nm to 1560 nm; a second optical fiber amplifier, connected with the first optical fiber amplifier, for providing a maximum amplification gain against an input light having a wavelength of 1570 nm to 1610 nm; and a tunable filter for passing an input light having a specific wavelength from the light output from the second optical fiber amplifier, the output light of the tunable filter is input to the first optical fiber amplifier, a tap coupler is established on an optical line through which the output light of the second optical fiber amplifier is forwarded to the first optical fiber amplifier.
To accomplish an object in accordance with a second embodiment of the present invention, there is provided an optical amplifier comprising: a first optical fiber amplifier, connected with an optical line in series, for supplying a maximum amplification gain against an input light having a wavelength of 1530 nm to 1560 nm; and a second optical fiber amplifier, connected with the first optical amplifier, for providing a maximum amplification gain again an input light having a wavelength of 1570 nm to 1610 nm.
To accomplish an object in accordance with a third embodiment of the present invention, there is provided an apparatus for generating L-band light source and an optical amplifier comprising: a first optical fiber amplifier for supplying a maximum amplification gain against an input light having a wavelength of 1530 nm to 1560 nm; a second optical fiber amplifier, connected with the first optical fiber amplifier, for providing a maximum amplification gain against an optical signal having a wavelength of 1570 nm to 1610 nm; a tunable filter for passing an input light having a specific wavelength from the light output from the second optical amplifier; a switching means for inputting the output light of the tunable filter or a specific input light selectively to the first optical fiber amplifier; and a tap coupler for receiving the output light of the second optical fiber amplifier and outputting a predetermined amount of light as an output light.
According to the above configuration of the present invention, the first optical fiber amplifier supplying a maximum amplification gain against an input light of a wavelength of 1530 nm to 1560 nm and the second optical fiber amplifier providing a maximum amplification gain against an optical signal of a wavelength of 1570 nm to 1610 nm are connected with each other in series so as to use the output light of the first optical fiber amplifier as a pumping light of the second optical fiber amplifier. Accordingly, it is possible to supply a satisfied amplification gain and a stable resonating operation against a L-band signal light, thus generating a good light source.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.